Читать книгу Parasitology - Alan Gunn - Страница 82

Some reports state that there are over 100 species of Babesia, whilst others suggest that there are somewhat fewer. Most species are tick borne parasites of mammalian erythrocytes although some parasitize bird red blood cells. Some Babesia species also parasitize other blood cells, such as lymphocytes and histiocytes. The genus Babesia is primarily of economic importance as parasites of cattle, sheep, and other domestic animals (Table 3.2). The most important species are Babesia bigemina, Babesia bovis, and Babesia divergens. Babesia microti is primarily a parasite of rodents but it also infects other mammals and is the principal cause of human babesiosis. For example, between 2006 and 2015, the incidence of human infections in New York State, USA, increased from 1.7 cases per 100,000 persons to 4.5 cases per 100,000 persons. It has been isolated from ticks in Europe and human cases are increasingly reported – and not just in immunocompromised individuals. Because ticks are vectors for various bacterial and viral diseases, it is common for those who contract babesiosis to suffer from co‐infections such as Lyme disease. Rather confusingly, some literature refers to this parasite as Theileria microti. Even more confusingly, there is a parasite referred to as Babesia cf. microti, Babesia vulpes and Theileria annae that has a similar distribution and causes severe disease in dogs. The ‘cf’ denotes that it is uncertain whether it is actually B. microti, a sub‐species, or a closely related but different species. In addition to tick vectors, transmission of B. microti, and B. cf. microti is also possible across the placenta. Dogs and other canines infected with babesiosis are reportedly capable of directly transmitting the infection in their bites.